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Four emitters based on the naphthyridine acceptor moiety and various donor units exhibiting thermally activated delayed fluorescence (TADF) were designed and synthesized. The emitters exhibited excellent TADF properties with a small ΔE ST and a high photoluminescence quantum yield. A green TADF organic light-emitting diode based on 10-(4-(1,8-naphthyridin-2-yl)phenyl)-10H-phenothiazine exhibited a maximum external quantum efficiency of 16.4% with Commission Internationale de L'éclairage coordinates of (0.368, 0.569) as well as a high current and power efficiency of 58.6 cd/A and 57.1 lm/W, respectively. The supreme power efficiency is a record-high value among the reported values of devices with naphthyridine-based emitters. This results from its high photoluminescence quantum yield, efficient TADF, and horizontal molecular orientation. The molecular orientations of the films of the host and the host doped with the naphthyridine emitter were explored by angle-dependent photoluminescence and grazing-incidence small-angle X-ray scattering (GIWAXS). The orientation order parameters (ΘADPL) were found to be 0.37, 0.45, 0.62, and 0.74 for the naphthyridine dopants with dimethylacridan, carbazole, phenoxazine, and phenothiazine donor moieties, respectively. These results were also proven by GIWAXS measurement. The derivative of naphthyridine and phenothiazine was shown to be more flexible to align with the host and to show the favorable horizontal molecular orientation and crystalline domain size, benefiting the outcoupling efficiency and contributing to the device efficiency.

Four bipolar molecules, named 1-, 2-, 3-, and 4-3cbzBIZ, composed of tricarbazole (3cbz) substituted benzimidazole, were synthesized and characterized.

In this study, we develop a steady state and time-dependent exciton diffusion model including singlet and triplet excitons coupled with a modified Poisson and drift-diffusion solver to explain the mechanism of hyper triplet-triplet fusion (TTF) organic light-emitting diodes (OLEDs). Using this modified simulator, we demonstrate various characteristics of OLEDs, including the J-V curve, internal quantum efficiency, transient spectrum, and electric profile. This solver can also be used to explain the mechanism of hyper-TTF-OLEDs and analyze the loss from different exciton mechanisms. Furthermore, we perform additional optimization of hyper-TTF-OLEDs that increases the internal quantum efficiency by approximately 33% (from 29% to 40%).

Triplet is like a double-edged knife, that can degrade or benefit the electroluminescence performances of organic light-emitting diodes (OLEDs), especially for blue light. Therefore, efficient triplet harvesting for triplet-triplet fusion (TTF) fluorescence emission is essential to achieving high-efficiency blue TTF-OLEDs, which are known for their excellent reliability. This study presents a hyper-TTF mechanism for maximizing triplet exciton usage and avoiding triplet-polaron quenching to generate more photons through Dexter energy transfer (DET) and TTF processes. Specially, a triplet tank layer (TTL) was introduced adjacent to the TTF emitting layer (EML). Efficient carrier recombination and triplet generation are confined to the TTL of the device. Most triplets were observed to undergo DET from the TTL to the TTF EML; they subsequently became singlets exhibiting delayed fluorescence. Furthermore, the triplet-polaron quenching is suppressed by inhibiting hole into the TTF EML. A record-high TTF-OLED efficiency was achieved with an external quantum efficiency of 15.4%.

Sorting is pivotal data analytics and becomes challenging with intensive computation on drastically growing data volume. Sorting on FPGA has shown superior throughput, but the limited in-system memory causes vast data transferring to/from external storage when handling a large dataset. We propose a two-directional sorting (2DSort) architecture which sorts data sequences on both horizontal and vertical directions. 2DSort significantly reduces the costly data transmission by tracking the data on FPGA and writes back the data to external storage when the final sorting position is determined. 2DSort shows average 38.5 percent runtime enhancement in comparison to state-of-the-art bigdata sorting engine on FPGA.

Developing a colloidal quantum-dot light-emitting device (QDLED) with high efficiency and good reliability is necessarily preliminary for the next-generation high-quality display application. Most QDLED reports are focused on efficiency improvement, but the device operational lifetime issue is less addressed and also the relevant degradation mechanisms. This study achieved a 1.72 times elongation in the operational lifetime and a 9 times improvement in the efficiency of QDLED by inserting a hole-transporting/electron-blocking poly(9-vinylcarbazole) (PVK) layer, which prevented operational degradation on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-secbutylphenyl))-diphenylamine)] (TFB) hole-transporting layer and also confined the electron in the QD-emitting layer. Although the TFB/PVK HTL structure is a well-known pair to enhance the device performance, its detailed mechanisms were rarely mentioned, especially for relative operational lifetime issues. Herein, a new insight behind operational lifetime elongation of QDLED is disclosed through various fundamental experiments including steady-state photoluminescence, transient electroluminescence and single-carrier only devices. Evidently, other than QD degradation, this study found that the other crucial factor that decreased the device lifetime was TFB-HTL degradation using steady-state photoluminescence and transient electroluminescence analyses. The PVK electron-only device exhibited a stable voltage value when it was driven by fixed current, which also affirmed that PVK has excellent electron-stability characteristics.

FPGA (Field Programmable Gate Array) has been adopted as an efficient acceleration platform to support high throughput queries to big database. This paper proposes a Reconfigurable Database Processor (RDP) to enable end-to-end query processing. The engines can be reconfigured to support different design parameters. The data processing modules are allocated into stages, and composed to generate the accelerator structure for queries. We further proposed a systematic flow to adapt the design of RDP to the requirements of different queries. The experiments on TPC-DS have shown that RDP attains 56.5% higher throughput over the conventional solution on CPU. When compared with the previous FPGA designs, RDP shows 23.8% advantage on the overall performance while saving 13.6% FPGA resources.

This study presented the effects of carrier-transporting layer (CTL) on electroluminescence (EL) performance of a blue phosphorescent organic light-emitting diodes (PHOLEDs) with electron transporting host based on three kinds of electron-transporting layers (ETLs) including 3-(4-biphenyl-yl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ), diphenyl-bis[4-(pyridin-3-yl)phenyl]silane (DPPS) and 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB) and two kinds of hole-transporting layers (HTLs) such as 4,4′-bis[N-1-naphthyl-N-phenyl-amino]biphenyl (NPB), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC). The carrier recombination and exciton formation zones in blue PHOLEDs strongly depend on the carrier mobility of CTLs and the layer thickness, especially the carrier mobility. Between ETLs and HTLs, the high electron mobility of ETL results in a lower driving voltage in blue PHOLEDs than the high hole mobility of HTL did. In addition, layer thickness modulation is an effective approach to precisely control carriers and restrict carriers within the EML and avoid a leakage emission of CTL. For CTL pairs in OLEDs using the electron transporting host system, ETLs with low mobility and also HTLs with high hole mobility are key points to confine the charge in EML for efficient photon emission. These findings show that appropriate CTL pairs and good layer thickness are essential for efficient OLEDs.

In this study, we report a bistriazoles derivative to be the wide bandgap host for blue emitters. In particular, this bistriazoles derivative possesses a wide bandgap of 4.0 eV and bipolar carrier transportation behavior. In addition, its bipolar behavior is classified to the rare case of electron-favorable bipolar carrier transportation, which was identified by the time-of-flight measurement and unipolar device. The electron mobility is little faster than hole one, which benefits the adjustment of carrier balance in the emitting layer. Employing to be the host of blue phosphorescent OLED, the device exhibits a high-efficiency performance with a 30.2%EQE.

Although phosphorescent and thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLED) exhibit high efficiency and long lifetime for red and green emission, blue OLED is still a bottleneck. In mass production, triplet-triplet emission (TTA) OLED is the main stream for reasonable lifetime together with limited efficiency. To improve the efficiency of blue TTA-OLED, a bilayer emitting layer (EML) was employed. Compared to single-EML device, external quantum efficiency of the bilayer OLED increased from 9.4% to 13.0%, which mainly resulted from the increase of delayed emission from 15.0% to 37% with enhanced TTA process.

Recently, Quantum-dot light-emitting diode (QLED) has attracted much attention due to narrow electroluminescence (EL) spectra, low driving voltage, tunable emission colors and simple fabrication. In conventional QLED structure, inorganic zinc oxide (ZnO) nanoparticles was usually used as electron transporting layer material by spin-coating. However, defects in solution-processed ZnO film may quench quantum dot (QD) emission and increase the driving voltage. In this study, we fabricated ZnO by sputtering process with the inverted structure. Compared to the QLED with solution-processed ZnO as the ETL, driving voltage of the device with sputtered-ZnO as the ETL significantly decreased from 7.04 V to 2.95 at current density of 20 mA/cm2, while the current efficiency remained at 11.46 and 11.70 cd/A at current density of 80 mA/cm2.

Lots of attentions owing to its superior properties such as narrow electroluminescence (EL) spectra, tunable emission colors, high luminance, and simple fabrication process. Typically, in a QLED, quantum dots (QD) layer is sandwiched by organic materials as hole transporting layer (HTL) and inorganic zinc oxide (ZnO) nanoparticles as electron transporting layer (ETL), respectively. Because the electron mobility of ZnO is typical higher than the hole mobility of organic material, it results in carrier unbalance and reduces the efficiency. Hence, it is important to improve the hole transporting ability to achieve charge balance condition for higher efficiency. In this study, we have fabricated green QLEDs with two different HTL materials. By using HTL with high mobility and suitable energy level, voltage decreased from 11.1 V to 5.8 V at 10 mA/cm2, together with enhancement of current efficiency from 21.8 cd/A to 58.1 cd/A, and external quantum efficiency from 5.94% to 16.0%, corresponding to 2.6-times improvement.

This study reported the effects of electron transport layer (ETL) thickness on light extraction in corrugated organic light-emitting diodes (OLEDs) and each layer in OLEDs exhibited a periodical corrugated structure, which was determined by depositing thin films on a glass substrate with a nanoimprinted blazed grating structure. The insight is that light extraction in corrugated OLEDs significantly depends on the ETL thickness. Varying the ETL thickness changed the distribution of carrier recombination and led to exciton formation and optical interference, thereby resulting in different attribution of optical loss modes in OLEDs, which increased or even decreased light extraction and device efficiency. Trapped light extraction from the surface plasmon polariton (SPP) and waveguide (WG) modes was identified by splitting the light into transverse electric and transverse magnetic emissions. Thus, the contributions from the individual SPP and WG modes to the external quantum efficiency (EQE) were distinctly clarified by comparing the experimental results with the theoretical calculations. At the ETL thickness of 115 nm, the corrugated OLED exhibited a significantly enhanced (1.83-fold) EQE compared to the planar one due to the effective extraction of trapped light from the SPP and WG modes. The EQE was enhanced by 0.5%, wherein 0.39% came from the WG mode and 0.11% came from the SPP mode.

New derivatives of trifluoromethyl benzene and tert-butyl disubstituted acridan or phenothiazine were designed and obtained by single-step synthesis, i.e., by Buchwald-Hartwig cross-coupling reactions of 1,3-dibromo-5-(trifluoromethyl)benzene with 3,7-di-tert-butyldimethylacridan, or 3,7-di-tert-butyl-10H-phenothiazine. The advantages in high thermal and photophysical characteristics were utilized in exciplex emission based OLEDs. In the optimal case, device showed maximum current, power, and external quantum efficiencies of 27.4 cd/A, 28.6 lm/W and 7.6%, respectively. Taking into account that successful employment of acridan or phenothiazine derivatives as donors in exciplex-forming systems remains scarce, the proposed design of donor compounds in this work shows their potential for successful implementation in complex emissive systems of OLEDs.

The efficient conversion of electron-hole (e-h) pairs into triplet excitons is a challenge for blue organic light-emitting diodes (OLEDs) based on triplet–triplet annihilation upconversion (TTAUC). The 25% fraction of e-h pairs that create singlet excitons represents a significant loss channel that can lead to parasitic red-shifted emission. In this study, an intermolecular intersystem crossing that relies on a “dark sensitizer” (DS) layer consisting of tris-(8-hydroxyquinoline)aluminum (Alq3) doped with tris[2-phenylpyridinato-C2,N]Iridium(III) (Ir(ppy)3) is demonstrated to enhance the TTAUC process. Carriers recombination and excitons generation are formed on Alq3 molecules. Alq3 singlet excitons are then quenched by the Ir(ppy)3 triplet state, followed by energy transfer to the Alq3 triplet state. The non-emissive, long-lived Alq3 triplets migrate from the sensitizer layer to an emitter layer where they undergo TTAUC to give blue fluorescence emission. This DS-TTAUC process promises no green emission from the Alq3. The efficiency of a blue OLED utilizing DS-TTAUC was improved by 34.2% compared to a standard TTAUC OLED. In addition, the device exhibited CIE coordinates of (0.15, 0.09). Furthermore, a high photoluminescence quantum yield fluorescence emitter is incorporated to enhance the singlet exciton emission in the emitter layer. A maximum external quantum efficiency of 7.54% can be achieved with recorded-high quantum yield of the TTAUC (ΦTTAUC) = 37.6% in solid state.

A corrugated indium zinc oxide thin film was fabricated on a glass substrate at room temperature for use in a blue phosphorescent organic light-emitting device (OLED) to facilitate device efficiency in term of the external quantum efficiency (EQE) of the device, which increased from 28.77% to 34.33% after the fabrication of the aforementioned layer. Furthermore, a remarkably high EQE of 52.51% was achieved through external light extraction by attaching a hemispheric macrolens on the substrate of the device. Consequently, the efficiency of the developed blue phosphorescent OLED became 1.83 times higher than that of a planar counterpart. Moreover, this finding was verified through theoretical analyses, that indicated the underlying light extraction physics was attributed to the efficient extraction of trapped light from the surface plasmon polariton, waveguide, and substrate modes. (submitted to Organic Electronics).

The enhanced device performance of blue quantum dot light-emitting diodes (QD-LEDs) was demonstrated; a positive aging process was used to improve electron transport and suppress electroplex emission, which results from the interface between the QD-emitting layer and the ZnO electron-transporting layer (ETL). This electroplex interface functions as a low-energy recombination center, leading to energy loss and further decreasing the device performance. Without the positive aging process, the QD-LED exhibited poor electrical and electroluminescent (EL) characteristics, as well as an EL spectrum containing a strong electroplex emission with a peak at 635 nm. A positive aging process was applied by dripping a surface active reagent on the cathode before device encapsulation. The active reagent treatment led to suppression of the electroplex emission and enhanced device performance by promoting Al atoms into ZnO ETL to facilitate electron transport at the QD/ZnO interface. Furthermore, static positive aging was investigated by assessing the QD-LEDs at different storage times to observe the maturing process. After 409-hrs of maturing, the QD-LEDs exhibited an optimal device performance with favorable CEmax and EQEmax values of 6.2 cd/A and 8.7%, respectively. At a current density of 1 mA/cm2, the QD-LED exhibited a maximum overall efficiency enhancement factor of 7.1 after the positive aging process. In particular, electroplex suppression was correlated with the enhancement of device performance, caused by an upgraded QD/ZnO interface, formed during the positive aging process, benefits the electron transport.

When applying the voltage pulses (6 V) to the organic light-emitting diode based on tris(8-hydroxyquinolinato) aluminium (Alq 3 ) as the electron transporting layer, current density and luminance increased by 16% and 20%, respectively, by providing the reverse bias (−16 V) during the off-period. By using displacement current measurement, we can deduce that such an enhancement resulted from the interfacial positive charges trapped at the Alq 3 /cathode interface, with the relaxation time ∼0.4 ms. By doping the organic material as the carrier trapping sites at Alq 3 /cathode interface, such current density and luminance increase can be further enhanced. 25% and 36% increase in current density and luminance was demonstrated with such driving technique, respectively.

In this study, we demonstrated a blue phosphorescent organic light-emitting diode (BPOLED) based on a host with two carbazole and one trizole (2CbzTAZ) moiety, 9,9′-(2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-1,3-phenylene)bis(9H-carbazole), that exhibits bipolar transport characteristics. Compared with the devices with a carbazole host (N,N’-dicarbazolyl-3,5-benzene, (mCP)), triazole host (3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole, (TAZ)), or a physical mixture of mCP:TAZ, which exhibit hole, electron, and bipolar transport characteristics, respectively, the BPOLED with the bipolar 2CbzTAZ host exhibited the lowest driving voltage (6.55 V at 10 mA/cm2), the highest efficiencies (maximum current efficiency of 52.25 cd/A and external quantum efficiency of 23.89%), and the lowest efficiency roll-off, when doped with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as blue phosphor. From analyses of light leakage of the emission spectra of electroluminescence, transient electroluminescence, and partially doped OLEDs, it was found that the recombination zone was well confined inside the emitting layer and the recombination rate was most efficient in a 2CbzTAZ-based OLED. For the other cases using mCP, TAZ, and mCP:TAZ as hosts, electrons and holes transported with different routes that resulted in carrier accumulation on different organic molecules and lowered the recombination rate.

Evaluation of insertion/deletion (InDel) regions by comparative chloroplast DNA (cpDNA) analysis of two endemic moth orchids, Phalaenopsis aphrodite and P. equestris, identified 15 highly variable cpDNA regions that could be served as useful markers for interspecific differentiation of moth orchids. In this study, we evaluated 31 cpDNA regions carrying simple sequence repeats (SSRs) or InDels from two moth orchids to reveal intraspecific markers for distinguishing the cultivars of P. equestris. In total, 18 of the cpDNA markers were variable among cultivars of P. equestris; 9 cpDNA markers were highly variable, with polymorphic information content ≥5.5. The petA-psbJ, psbB-psbT and rps16-trnQ markers showed the best discriminatory power; 11 P. equestris cultivars could be separated into at least five groups. From the sequences for six selected cpDNA regions, the rps16-trnQ and psbB-psbT intergenic spacers were the best DNA barcodes; 11 P. equestris cultivars could be separated into six distinct groups. Phylogenetic analysis revealed that P. equestris cultivars have evolved into two major lineages, and the species in the Stauroglottis and Amboinenses sections are in a non-monophyletic relationship. We have revealed a set of cpDNA markers that could be used for intraspecific identification and phylogenetic study of P. equestris cultivars.

A new emission mechanism was proposed to enhance the OLED operation lifetime by using exciplex emission to sensitize the triplet-triplet annihilation blue emission. 3-times improvement in operation lifetime was achieved due to the alleviation of electron accumulation at the interface of the hole-transporting layer and the emitting layer.

In this paper, we demonstrated the changes of electrical and optical characteristics of a phosphorescent organic light-emitting device (OLED) with tris(phenylpyridine)iridium Ir(ppy)3 thin layer (4 nm) slightly codoped (1%) inside the emitting layer (EML) close to the cathode side. Such a thin layer helped for electron injection and transport from the electron transporting layer into the EML, which reduced the driving voltage (0.40 V at 100 mA/cm2). Electroluminescence (EL) spectral shift at different driving voltage was observed in our blue OLED with [(4,6-di-fluoropheny)-pyridinato-N,C2′]picolinate (FIrpic) emitter, which came from the recombination zone shift. With the incorporation of thin-codoped Ir(ppy)3, such EL spectral shift was almost undetectable (color coordinate shift (0.000, 0.001) from 100 to 10,000 cd/m2), due to the compensation of Ir(ppy)3 emission at low driving voltage. Such a methodology can be applied to a white OLED which stabilized the EL spectrum and the color coordinates ((0.012, 0.002) from 100 to 10,000 cd/m2).

Comparative analysis of chloroplast DNA (cpDNA) between two endemic moth orchids in Taiwan, Phalaenopsis aphrodite subsp. formosana and P. equestris, previously revealed many evolutionary hotspots. In this study, we explored 27 pre-screened cpDNA regions to evaluate molecular markers for distinguishing Phalaenopsis species. Fifteen cpDNA markers were highly variable among moth orchids, with polymorphic information contents ≥8.0. The rps16-trnQ marker showed the best discrimatory power which 15 endemic moth orchids could be successfully separated into 13 groups. From the sequences of the seven selected cpDNA regions, the rps16-trnQ intergenic spacer was the best DNA barcode which 19 endemic moth orchids could be completely distinguished. The petN-psbM intergenic spacer could be better used as a DNA barcode to differentiate P. aphrodite subsp. formosana and P. amabilis. Additionally, the inheritance mode of cpDNA in moth orchids was maternally predominated. Phylogenetic analysis revealed non-monophyletic relationships below the Phalaenopsis genus level. In summary, we have revealed a set of cpDNA markers that could be used for identification and phylogenetic study of Phalaenopsis orchids.

Operation lifetime of a blue OLED exhibiting triplet-triplet annihilation increased by 89.3% with the incorporation of 10% assistant host in the emitting layer, which increased diffusion length of singlet exciton, reduced the quenching of triplet exciton, and blocked the triplet pair diffusion.

Aim This study investigated the extent to which the job demands and job control of nurses were related to their work–life balance. Background The inability to achieve work–life balance is one of the major reasons for the declining retention rate among nurses. Job demands and job control are two major work domain factors that can have a significant influence on the work–life balance of nurses. Method The study measured the job demands, job control and work–life balance of 2040 nurses in eight private hospitals in Taiwan in 2013. Results Job demands and job control significantly predicted all the dimensions of work–life balance. Job demands increased the level of work–life imbalance among nurses. While job control showed positive effects on work/personal life enhancement, it was found to increase both work interference with personal life and personal life interference with work. Conclusion Reducing the level of job demands (particularly for psychological demands) between family and career development and maintaining a proper level of job control are essential to the work–life balance of nurses. Implications for nursing management Flexible work practices and team-based management could be considered by nursing management to lessen job demand pressure and to facilitate job engagement and participation among nurses, thus promoting a better balance between work and personal life.

We demonstrated device performances of exciplex organic light emitting diodes (OLEDs) by using 4, 4′, 4”-tris(N-3-methyphenyl-N-phenyl-amino) triphenylamine (m-MTDATA) and 4,7-diphenyl-1,10-phenanthroline (Bphen) as electron donor and acceptor materials, respectively with different emitting layer (EML) thicknesses. The maximum current efficiency and external quantum efficiency (EQE) of the optimized OLEDs are 11.3 cd/A and 4.02%, respectively. Transient electroluminescence (TrEL) was used to understand the carrier and exciton dynamics in the OLEDs. It was found that the thinner EML exhibited a shorter decay time in such devices.

We demonstrated a blue phosphorescent organic light-emitting diode with the maximum current efficiency and power efficiency of 57.4 cd/A and 51.6 lm/W, respectively, based on trizaole derivatives as the host of the emitting layer.

A novel carbazole-triazole derivative was used as a bipolar host of a phosphorescent blue organic light-emitting diode doped with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolmato)iridmm(III) (FIrpic). Maximum current efficiency, power efficiency, and external quantum efficiency of this blue phosphorescent OLED reached 50.30 cd/A and 25.03%, respectively. Efficiency roll-off was alleviated due to the wide recombination zone, and current efficiency slightly reduced to 46.67 cd/A at 1000 cd/m2.

Recently, ‘Liquid crystal display (LCD) vs. organic light-emitting diode (OLED) display: who wins?’ has become a topic of heated debate. In this review, we perform a systematic and comparative study of these two flat panel display technologies. First, we review recent advances in LCDs and OLEDs, including material development, device configuration and system integration. Next we analyze and compare their performances by six key display metrics: response time, contrast ratio, color gamut, lifetime, power efficiency, and panel flexibility. In this section, we focus on two key parameters: motion picture response time (MPRT) and ambient contrast ratio (ACR), which dramatically affect image quality in practical application scenarios. MPRT determines the image blur of a moving picture, and ACR governs the perceived image contrast under ambient lighting conditions. It is intriguing that LCD can achieve comparable or even slightly better MPRT and ACR than OLED, although its response time and contrast ratio are generally perceived to be much inferior to those of OLED. Finally, three future trends are highlighted, including high dynamic range, virtual reality/augmented reality and smart displays with versatile functions.